Manufacture of high-voltage cable



Nov. 23, 1965 v. F. VOLK 3,219,501

MANUFACTURE OF HIGH-VOLTAGE CABLE Original Filed May 16. 1961 2 Q i FIG. I 'Q i 1 i0\ h l I4 21 I9 I6 |7 .|YgmL-2v3 24 A I3 `l l l l y u 12Y" /f f d i Y Y g f/ y// xx 63 3 7| i 64 Eig; M I i... im gs Ei* 38 mm52m 4n||i| 34 4| 39 49 5| 66 36 lil *j lil I!! 70 48 :EEEE-:Ei-s' g {g}A fl gg; :lil: se

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98 7 e4 88 99 97 86 a9 new 6L 1 Il Llll/l/ JI' l F l G 3 INVENTOR m VUMUnited States Patent i ice 3,219,501 Patented Nov. 23, 1965 3,219,501MANUFACTURE F HGH-VOLTAGE CABLE Victor F. Volk, Hastings on Hudson,NSY., assigner, by

mesne assignments, to Anaconda Wire and Cable Company, a corporation ofDelaware Original application May 16, 1961, Ser. No. 82,819, now PatentNo. 3,080,446, dated Mar. 5, 1963. Divided and this application May 28,1962, Ser. No. 205,815

2 Claims. (Cl. 15d- 53) My invention relates to pipe-type cable andparticularly to the manufacture of pipe-type cable having theinsu-lation thereof protected by a dielectric skid wire.

In the manufacture of high voltage cables of the type where electricconductors are wrapped with a plurality of layers of insulating materialsuch as, for example, a plurality of paper tapes and subsequently pulledinto a steel pipe which is then lled with an insulating fluid, such ashydrocarbon oil or pressurized nitrogen it is known to protect the cablecores during the pulling operation with spiral windings of bronze skidwires. These known skid wires are most conveniently formed in half-roundsections with the hat side laid against the insulation and the roundedsurface making low-friction contact with the inner walls of the pipe.

Cables of the type described in my application and in my applicationSerial Number 82,819, now U.S. Patent No. 3,080,446, of which thepresent application is a division are generally known as pipe-typecables and will be so styled in this application although it will beunderstood that my invention is not limited by the nature of theenclosure comprising the containing element of my cable. Most commonly,said containing element is an eight-inch steel pipe but it may becomprised of a nonmetallic material such as cement or plastic and mayhave various degrees of exibility.

The known construction of pipe-type cables having bronze skid Wires hasproven to be satisfactory in almost all respects but has the one seriousshortcoming that the currents induced in the skid wire may constitute aserious power loss accounting, in some instances, to as much as 2% ofthe power losses in the cable.

It is an object of my invention to provide a pipe-type cable wherein theskid wire is free from induced current losses.

It is another object of my invention to provide a pipetype cable inwhich the skid wire will remain wrapped around the insulated conductorin the event of an accidental severing of the skid wire duringinstallation.

l have invented a high-voltage electric cable comprising a conductor,electrical insulation surrounding said conductor, and a dielectric skidwire applied spirally over the insulation. The outer surface of my skidwire is preferably in compression so that the skid wire grips theinsulation and will not unwind from the insulation even if it should bebroken at some point. The insulated conductor and the skid wire of mycable are surrounded by a tubular container, overall. In a preferredembodiment of my invention the skid wire is comprised of linearpolyethylene and in another preferred embodiment it is comprised ofnylon. My cable has an electric shield over the insulation and in apreferred embodiment a plurality of conducting means are spaced atintervals along the skid wire making electrical contact between theshield and the tubular container which in this embodiment is metallic.The conducting means will preferably extend for a complete turn of theskid wire so as to be certain to contact the container regardless of theposition of rotation of the insulated conductor.

I have also invented a process for manufacturing a pipetype cablecomprising the steps of insulating an electrical conductor, extruding alength of dielectric skid wire, forming the skid wire into a helix withan inside diameter not substantially larger than the diameter over theinsulated conductor and wrapping the skid wire around the insulated wirewhile compressing the outer surface of the skid wire. Advantageously,the skid wire is annealed and cooled while in a helical form. When theskid wire is comprised of linear polyethylene, I prefer to anneal it ata temperature of 220-230" F.

A more thorough understanding of my invention will be obtained from astudy of the appended drawing.

In the drawing:

F-IG. l is a lengthwise cut-away View of a cable made in accordance withmy invention.

FIG. 2 is a schematic plan view of a process for forming the skid wireof my invention.

FIG. 3 is a schematic elevation of a process for applying the skid wireof my invention.

Referring now to FIG. 1:

A pipe-type cable designated generally at 10 has a conductor 11 wrappedwith strand shielding 12 of semiconducting carbon black paper andinsulated with a heavy wall 13 built up of a plurality of layers ofinsulating paper. The wall of insulation 13 is covered with a conductingshield 14 of copper tapes. The shield 14 is shown applied directly overthe insulation 13 but there may be intermediate layers of carbon blacktape or of impervious tapes applied for the purpose of preventingmoisture from entering the insulation 13 during the processes ofstoring, shipping, and installing the cable. The conductor 11, strandshielding 12, insulation 13, shield 14, and any intermediate layersbetween the insulation 1-3 andthe .shield 14 constitute .a unit 16 thatI shall hereinafter call an 4insulated conductor. Over the insu-latedconductor 16 I have applied two skid wires 17, 18, 180 apart. Although Ihave chosen to apply two skid wires my invention is not restricted tothis number. For example a single skid wire might be :applied at 1/2 thepitch that I have chosen for my two wires or a larger number such asthree or four might be applied having a longer pitch.

The skid wires 17, 18 have each a substantially flat surface 19 facingthe insulated conductor 16 and a rounded outer surface 21. A steel pipe22 constitutes a tubular container for the insulated conductor 16covered by skid wires 17, 18. Although for the sake of simplicity I haveshown only one insulated conductor 16 in the pipe 22, three suchinsulated conductors are generally inclosed in the pipe, each of theconductors being identical to the insulated conductor 16 yand havingskid wires applied identically to the skid wires 17, 18. The pipe 22 isfilled with an insulating iluid such as an insulating oil which canpenetrate the insulation 13 or a gas such as nitrogen maintained undersuper-atmospheric pressure.

It is a feature of my invention that the skid wires 17, 18 are comprisedof a dielectric, or insulating material of which linear polyethylene isa preferred example. The purpose of the skid wires 17, 18 is to protectthe shield 14 .and the insulation 13 from the effects .of abrasionagainst the pipe 22 during installation. The method of installation-requires that the insulated conductor 16 lbe unwound from reels anddragged into the pipe 22 by means of a cable fastened to the conductor11. Commonly three insulated conductors such as 'the one designated 16.are pulled into the pipe 22 simultaneously from three diierent reels.

Prior to my invention bronze armor wires similar to my skid wires 17, 1Swere wrapped around the core 16 to protect the insulated conductorduring installation. These known armor wires had the disadvantages thatthey readily picked up induced electric currents from the conductor 11,that they added considerably to the weight of the insulated conductor16, and that they had a relatively high coefficient of friction againstthe walls of the pipe 22 compared to the skid wires 17, 18 of myinvention. My skid wires 17, 18 are formed of a tough, resinous materialwhich will not transmit electric current, has high resistance toabrasion, and has a very low coefficient of friction. Polyethylene maybe used for my skid wires 17, 18 or the vinyl resin known as rigidpolyvinyl chloride. However, I prefer to form my skid wires from linearpolyethylene or from nylon. By linear polyethylene I refer topolyethylene resin with a pressure of about 0.941 or higher. Thispolyethylene is made by a low density process such as the Zieglerprocess and is extremely tough and abrasion resistant.

Nylon is a generic term for a family of polyamide resins characterizedby high tensile strength, tou-ghness and abrasion resistance and by alow coefficient of friction. Both the linear polyethylene and nylonwhich I prefer for the .skid wires of my invention are well knownmaterials of commerce for which I make no claims of invention as such.

Where the pipe 22 is a metallic pipe and it is considered desirable toground the shield 14 periodically along the length of the cable, one orboth of the skid wires 17, 18 are wrapped at spaced intervals with metalbands 23, 24. The bands 23, 2.4 are conveniently applied to the skidwires 17, 18 at spaced intervals prior to Ithe application of the skidwires to the insulated conductor 16. Although I prefer to use bands 23,24 made fro-m bronze or stainless steel it will be understood thathelical windings of metal wire may be substituted for the bands or thesurface of the skid wire may be coated with conducting paint. One of theprincipal advantages of my invention resides in the high electricalresistance of the dielectric skid wires 17, 18 as compared with thebronze arrnor wires known to prior ar-t. This high electrical resistanceprevents induced electrical currents in the skid wires. It is important,therefore, that the conducting bands 23, 24 should be applied only atspaced intervals `on the skid wires 17, 18 and not from a continuousconducting path along the cable. By spacing my conducting means 23, 24 Ieffectively prevent any appreciable power losses from induced currents.The pipe-type cable constitutes relatively expensive engineeringinstallation requiring considerable advance Aplanning and preparationfor a Successful installation. If, in the course of pulling theinsulated conductor 16 into the pipe 22, any accident were to befall theconductor 16 requiring the withdrawal of the conductor from the pipe andits return to the factory the financial losses would be great. Such anaccident would be the severing of one or both of the skid wires 17, 18due to cutting edges on the inside of the pipe 22 or to foreign objectsin the pipe. If the skid wires 17, 18 were merely wrapped around theinsulated conductor 16 the outside surface 21 of the skid wires 17, 18would be under tension and the inside surface 19 would be undercompression in accordance with well known bending formulas and the skidwires 17, 18 would spring away from the insulated conductor 16 at anypoint where a break should occur and would, indeed, become loose for thefull length of the cable. It would be impossible to make repairs in thefield where the skid wires 17, 18 had become loosened over any longlength of the cable. It should be further noted that the -skid wires 17,18 protect the cable not only during the process of pulling theinsulated conductor 16 into the pipe 22 but also after the pipe has beenlled with insulating iiuid and the cable energized the skid wires 17, 18are relied upon to protect the shield 14 and insulation 13 during thewrithings that take place because of expansion in the conductor 11caused by current loading. If the skid wires 17, 18 were applied so asto produce tension in the outside surface 21 not only would the skidwires tend to spring open if they were broken but any sm-all cuts orabrasions of the surface would become focal points for tearing under theinliuence of the tension or stretch in the surface and such tearingmight eventually extend through the entire thickness of the skid wireand result in a break. I have overcome the above mentioned obstacles byso applying the skid wires 17, 18 that the outer surfaces are incompression rather than tension. This has the twofold advantage ofmaking the skid wires more resistant to abrasive a-ction and ofguaranteeing that they will remain snugly 4bound to the insulatedconductor 16 even though a break may occur at some point. If a breakshould occur in a skid wire in the field it is a relatively simplematter to repair it so long as the skid wire does not spring open andthe delay and expense of returning -the cable to the factory is avoided.

In order to produce compression rather than tension in the outer surfaceof my skid wires 17, 18 I first form them into a helix and anneal themin this form. This can best be understood by reference to FIG. 2. InFIG. 2 the skid wire 17 that has preferably been formed by extrusioninto a half-round or similar section is paid from a reel 31 throughvertical guide rolls 32 onto a polished mandrel 33. The mandrel 33 ismounted in a bearing 34 and driven through the shaft 36 by spur gears37, 38. The shaft 36 is, in turn, driven by a motor, not shown. As thepolished mandrel 33 rotates, turns 39 of the skid wire 17 form aroundthe mandrel and are urged to the right by the wedging action of block41. As the turns 39 slide down the mandrel 33 they pass through an oven42 which heats them to a temperature sutiicient to anneal the skid wire17 but not sufiicient to cause distortion or to cause the turns 39 toadhere to each other or to the mandrel 33. In the case of linearpolyethylene the length and temperature of the oven 42 are sufficient toraise the linear polyethylene skid wire to a temperature of 220-230" F.As the turns 39 of the skid wire 17 leave the oven 42 they pass under acooling spray 43 of water from a spray head 44 fed by a water pipe 46 toa source of cooling water not shown. The cooling spray 43 is caught in atrough 47 drained by a pipe 48. In order to prevent the cooling waterfrom cooling the mandrel 33 in the oven 42 an insert 49 of materialhaving a low heat conductivity divides the mandrel 33 from a polishedextension 51 which supports the turns 39 while they are in the coolingspray. The insert 49 has the same diameter as the mandrels 33 and 51 andis preferably made of Teflon which is a good heat insulator, 4and alsohas a low coefficient of friction to permit sliding of the turns 39. Asthe turns 39 slide from the cool end of the mandrel 51 they are guidedby a chute 52 through a traverse 53 tonto a reel 54. The reel 54 isdriven by means of the sprockets 56, 57 and chain 58 by the motor 59powered through the slip rings 61, 62. The reel 54 is housed in a frame63 driven through a sprocket 64, chain 66, sprocket 67, shaft 68,sprocket 6g, chain 76, and sprocket 71 to rotate at the same speed asthe mandrels 33, 51. The mandrel 33, 49, 51 has a diameter less than thediameter of the insulated conductor 16 and is so chosen that when theskid wires 17, 18 are wrapped around the insulated conductor 16 theouter surface 21 of the skid wires will be in compression and thetension on the inner surface 19 of the skid wires 17, 18 will not be sogreat as to cause tearing at this surface. With a half-round skid wire17 of 1/4 inch diameter, I prefer to use a mandrel diameter about of theinsulated conductor diameter but I do not wish to be limited to thisratio since the optimum dimensions will be inuenced by the particularmaterial of the skid wire, by its cross-sectional dimensions, and by thepitch at which the skid wire is applied to the insulated conductor.

The skid wires 17, 18 are applied to the insulated conductor 16 by meansof a planetary cabler 81 (FIG. 3) with the reel 54 mounted in a cradle82 which remains horizontal or rotates slowly 4as desired, because ofthe planetary gear 83 rotated through the idler 84 against a xed gear 86by the mounting plate 87. The size of the fixed gear 86 can be varied inrelation to the planetary gear 83 to compensate in known manner for thedifference between the diameter of the insulated conductor 16 and thecoil 17. The skid Wire 18 is shown similarly mounted on the cabler 81. Arotating die 88 is driven through the sprocket 89, chain 91, sprocket92, shaft 93, sprocket 94, chain 96 and sprocket 97 (which is itselfdriven by a chain and motor not shown) at the same speed as the mountingplate 87` The die 88 has helical grooves 98, 99 which guide the skidwires 17, 18 in helical form around the insulated conductor 16. Becauseof the grooves 98, 99 in the die 8S the skid wires 17, 1S are fir lygripped during the wrapping operation and the necessary force is easilyapplied to increase the diameter of the helix and put the outer surfaceof the skid wires in compression.

Iclaim:

1. In the process of manufacturing a pipe-type cable comprising aninsulated conductor having a predetermined diameter, the steps of:

(A) extruding a length of dielectric skid wire,

(B) continuously wrapping said skid wire around a mandrel to form ahelix having a diameter smaller than the diameter of said conductor,

(C) continuously Sliding said helix from said mandrel,

(D) while on said mandrel continuously annealing and, while on saidmandrel, subsequently cooling said helix,

(E) and then immediately continuously taking up a length of the helixedwire on a reel, said length being great compared to the length of saidmandrel, and

(F) wrapping said skid wire around the insulated con- `ductor whilecompressing the outer surface of said skid wire.

2. In the process of manufacturing a pipe-type cable comprising aninsulated conductor having a predetermined diameter, the steps of:

(A) extruding a length of linear polyethylene skid w1re,

(B) continuously Wrapping said skid wire around a mandrel to form ahelix having a diameter smaller than the diameter of said conductor,

(C) continuously sliding said helix from said mandrel,

(D) While on said mandrel, continuously annealing said helix at atemperature of 220-230 F. and, While on said mandrel, subsequentlycooling said helix,

(E) and then immediately continuously taking up a length of the helixedwire on a reel, said length being great compared to the length of saidmandrel, and

(P) wrapping said skid wire around the insulated conductor Whilecompressing the outer Surface of said skid wire.

References Cited by the Examiner UNITED STATES PATENTS 8/ 1947 Roberts156-144 XR 8/1947 Morgan.

2,628,214 2/1953 Pinkney etal.

3,091,261 5/1963 Waddell 156-143 XR EARL M. BERGERT, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,219,501 November 23, 1965 Victor P. Volk It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

In the heading to the drawing, line 3, and in the heading to the printedspecification, line 6, for "May 16, 1961",

each occurrence, read Jan. 16, 1961 column 3, line 10, for "pressure"read density line 11, for "density" read pressure line 39, for "from"read form Signed and sealed this 2nd day of August 1966 (SEAL) Attest:

ERNEST W. SW'IDER EDWARD I. BRENNER Attesting Officer Y Commissioner ofPatents

1. IN THE PROCESS OF MANUFACTURING A PIP-TYPE CABLE COMPRISING ANINSULATED CONDUCTOR HAVING A PREDETERMINED DIAMETER, THE STEPS OF: (A)EXTRUDING A LENGTH OF DIELECTRIC SKID WIRE, (B) CONTINUOUSLY WRAPPINGSAID SKID WIRE AROUND A MANDREL TO FORM A HELIX HAVING A DIAMETERSMALLER THAN THE DIAMETER OF SAID CONDUCTOR, (C) CONTINUOUSLY SLIDINGSAID HELIX FROM SAID MANDREL, (D) WHILE ON SAID MANDREL CONTINUOUSLYANNEALING AND, WHILE ON SAID MANDREL, SUBSEQUENTLY COOLING SAID HELIX,(E) AND THEN IMMEDIATELY CONTINUOUSLY TAKING UP A LENGTH OF THE HELIXEDWIRE ON A REEL, SAID LENGTH BEING GREAT COMPARED TO THE LENGTH OF SAIDMANDREL, AND (F) WRAPPING SAID SKID WIRE AROUND THE INSULATED CONDUCTORWHILE COMPRESSING THE OUTER SURFACE OF SAID SKID WIRE.